1. Field of the Invention
The present invention relates to the field of integrated circuit chips; more specifically, it relates to a method of testing integrated circuit chips having Dynamic Random Access Memory (DRAM) embedded in logic using processor based Built-In-Self-Test.
2. Background of the Invention
Advanced integrated chips having a logical function such as gate arrays, microprocessors, Digital Signal Processors (DSP) and Application Specific Integrated Circuits (ASIC) require DRAMs embedded in the logic to function. BIST was originally developed for testing logic circuits and has been extended to testing embedded DRAMs as well.
Typical embedded DRAMs are comprised of multiple blocks of memory cell arrays. Testing of embedded DRAMs requires special test patterns designed to identify specific types of failures. One test of particular importance for embedded DRAMs cells using capacitive storage node devices is the retention time test. Retention time is the time a memory cell will hold its state before charge leaking off the storage node renders determination of the state of the cell uncertain.
Retention time testing requires reading a pattern into a block, pausing the test for a fixed amount of time, and reading out a pattern and comparing the readout pattern to an expected pattern. This sequence of write, pause, read and compare is repeated sequentially for each block of memory cell arrays in the embedded DRAM. The pause time is typically 1000 times longer than the write step or the read and compare step.
As the size of embedded DRAMs increase and especially the number of blocks of memory cell arrays per DRAMs increase, test times also increase. Test times have become a significant cost adder to gate arrays, microprocessors, DSPs and ASIC because of the added test equipment required. Increased test times have also had an adverse effect on productivity.
Therefore, there is a need in the industry for a method to reduce the amount of time to test embedded DRAM in such integrated circuit chips as gate arrays, microprocessors, DSPs and ASICs.